Israel insisted Monday it will do whatever it must to stop Iran from getting a nuclear weapon, even as the visiting U.S. defense chief promised tougher international sanctions if Tehran spurns an offer of talks.

U.S. Defense Secretary Robert Gates tried to reassure Israeli leaders that President Barack Obama is not naive, and he said the offer to bargain with Iran isn't good indefinitely. After meeting with Gates, Israeli Defense Minister Ehud Barak suggested his country's patience is limited, saying — three times — that Israel would not rule out any response.

"We clearly believe that no option should be removed from the table," Barak said, referring to the unstated possibility that Israel might launch a pre-emptive attack to thwart Iran's nuclear development.

Differences between Israel and the U.S. over how to handle a looming Iranian nuclear threat dominated Gates' brief stop in Jerusalem. And later, in neighboring Jordan, Gates was blunt in describing what Iran might expect if it refuses the offer of international arms control talks this year, or walks away from Obama's wider offer of better relations with Washington.

"If the engagement process is not successful, the United States is prepared to press for significant additional sanctions," Gates said. He added that the United States would try to abandon the current policy of gradual international pressure, where layers of generally mild sanctions have been added as each time Iran flouted international demands.

"We would try to get international support for a much tougher position," Gates said. He added: "Our hope remains that Iran would respond to the president's outstretched hand in a positive and constructive way, but we'll see."

While the United States also reserves the right to use force if need be, the Obama administration is playing down that possibility while it tries to draw Iran into talks. Gates said Washington still hopes to have an initial answer in the fall about negotiations.

"The timetable the president laid out still seems to be viable and does not significantly raise the risks to anybody," Gates said in Israel.

Israeli Prime Minister Benjamin Netanyahu has said he hopes to work out policy disagreements with the U.S. during a series of meetings this week with high-profile American envoys. Gates was the second in a parade of Americans coming to Israel this week, and the only one for whom Israel's expansion of Jewish settlements was not a primary topic.

Netanyahu's office said that during talks with Gates, Netanyahu "reiterated the seriousness (with) which Israel views Iran's nuclear ambitions and the need to utilize all available means to prevent Iran from achieving a nuclear weapons capability."

The United States contends that a strike would upset the fragile security balance in the Middle East, perhaps triggering a new nuclear arms race and leaving everyone, including Israel and Iran, worse off.

Iran has long insisted it is merely trying to develop nuclear reactors for domestic power generation. Israeli leaders fear the U.S. is prizing outreach to Iran over its historic ties to Israel and appears resigned to the idea that Iran will soon be able to build a nuclear weapon.

Obama says he has accepted no such thing.

Both Barak and Gates said time is short, and Gates stressed that any negotiations would not become cover for Iran to run out the clock while it perfects a nuclear weapon.

"I think we're in full agreement on the negative consequences of Iran obtaining this kind of capability," Gates said. "I think we are also agreed that it is important to take every opportunity to try and persuade the Iranians to reconsider what is actually in their own security interest."

Obama pledged a new outreach to Iran during last year's presidential campaign. Aides say the recent election-related political upheaval in Iran has complicated, but not derailed, that effort.

On Sunday, Secretary of State Hillary Rodham Clinton implicitly urged Israel to set aside any plans it might have for attacking Iran, saying she hopes the Jewish state understands the value of American attempts at diplomacy.

Speaking on NBC's "Meet The Press," Clinton also said she would not reveal any specifics of a possible "defense umbrella" to protect Mideast allies against an eventual Iranian bomb.

The umbrella idea, which Clinton offhandedly mentioned last week, has fueled Israel's uncertainty over U.S. policy under Obama even though Clinton later backpedaled.

Iran rejects the idea of a U.S. defensive umbrella to protect Washington's regional allies against a nuclear Iran. Foreign ministry spokesman Hasan Qashqavi told reporters Monday that "there is no need" for a U.S. defensive umbrella, just for Washington to tell Israel to "dismantle its own 200 nuclear warheads."